Musnad Ahmad 28:289

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Habib, who said: I heard Abu al-‘Abbas saying: I heard ‘Abdullah ibn ‘Amr narrating: That a man came to the Prophet, may Allah bless him and grant him peace, seeking his permission for Jihad. He said: "Are your parents alive?" He said: "Yes." He said: "Then in them, strive [perform Jihad]."